Grasslands In China Research Articles

Response of net primary production to land use and land cover change in mainland China since the late 1980s

Land use and land cover patterns in mainland China have substantially changed in the recent decades under the economic reform policies of the government. The terrestrial carbon cycle, particularly the net primary productivity (NPP), has been substantially changed on both local and national scales. With the growing concern over the effects of the terrestrial carbon cycle on global climate changes, the impacts of land use and cover change (LUCC) on NPP need to be understood. In this study, variations in NPP caused by LUCC (e.g., urbanization and conversion of other land use to forest and grassland) in mainland China from the late 1980s to 2015 were evaluated based on land cover datasets and NPPs simulated from the Carnegie–Ames–Stanford Approach model. The results indicate that the national total losses in NPP attributed to urbanization reached 1.695 TgC between the late 1980s and 2015. A large proportion (63.02%) of the total losses was due to the transformation from cropland to urban land. Urban expansion decreased the monthly and total NPPs over southern China, which includes the South China Region, Southwest China Region, and the middle and lower regions of the Yangtze River. However, the total NPP increased in the majority of urbanized areas in Northern China, including the Huang–Huai–Hai Region, Inner Mongolia Region (MGR), Gan-Xin Region (GXR), and Northeast China Region; monthly NPP in GXR and MGR increased throughout the year. By contrast, the conversion to grassland or forestland increased the monthly and total NPPs of Northern China, suggesting that returning to forestland and grassland could increase the carbon sequestration capacity of terrestrial ecosystems in mainland China. Among the sub-regions, the Loess Plateau Region contributed the largest increase in NPP, which was prompted by the conversion to grassland and forestland.

Asymmetric effects of daytime and nighttime warming on spring phenology in the temperate grasslands of China

Understanding the spring phenology of temperate grasslands and its response to climate change are crucial for diagnosing the responses of ecosystem to regional climate change and projecting regional ecosystem carbon exchange. Using NDVI data from 1982 to 2015, this study investigated the changes of the start date of the vegetation growing season (SOS) for the temperate grasslands of China, and explored the possible effects of average monthly Tmax, Tmin and total precipitation on the SOS across different grassland vegetation types. We improved on prior studies of climate change in China’s temperate zone by focusing only on grasslands unchanged over this extended study period. The results showed that the SOS significantly advanced at a rate of 1.84 days/decade from 1982 to 2015, controlled mainly by spring precipitation and spring and winter temperatures, with differing degrees of influence among vegetation types. On average, an increase of 10 mm in spring precipitation would advance SOS by 1.7 days across the temperate grasslands of China. Although warmer temperatures generally led to advanced SOS, this study revealed for the first time that the seasonal effects of daytime and nighttime warming on the SOS of temperate grasslands in China were asymmetric, with Tmax more influential in winter and Tmin more influential in spring. An increase of 1 °C in winter Tmax and spring Tmin would advance SOS by 0.42 and 1.34 days, respectively, compared with effects of 0.24 or 0.64 days for 1 °C increases in winter Tmin or spring Tmax. Given the global asymmetry in daytime and nighttime warming, this study highlights the asymmetric effects of daytime and nighttime warming on the SOS of temperate grasslands in China, and suggests that the impacts of seasonal Tmax and Tmin should be considered separately in the SOS modules of terrestrial ecosystem models for temperate grasslands.

Joint structural and physiological control on the interannual variation in productivity in a temperate grassland: A data-model comparison.

Given the important contributions of semiarid region to global land carbon cycle, accurate modeling of the interannual variability (IAV) of terrestrial gross primary productivity (GPP) is important but remains challenging. By decomposing GPP into leaf area index (LAI) and photosynthesis per leaf area (i.e., GPP_leaf), we investigated the IAV of GPP and the mechanisms responsible in a temperate grassland of northwestern China. We further assessed six ecosystem models for their capabilities in reproducing the observed IAV of GPP in a temperate grassland from 2004 to 2011 in China. We observed that the responses to LAI and GPP_leaf to soil water significantly contributed to IAV of GPP at the grassland ecosystem. Two of six models with prescribed LAI simulated of the observed IAV of GPP quite well, but still underestimated the variance of GPP_leaf, therefore the variance of GPP. In comparison, simulated pattern by the other four models with prognostic LAI differed significantly from the observed IAV of GPP. Only some models with prognostic LAI can capture the observed sharp decline of GPP in drought years. Further analysis indicated that accurately representing the responses of GPP_leaf and leaf stomatal conductance to soil moisture are critical for the models to reproduce the observed IAV of GPP_leaf. Our framework also identified that the contributions of LAI and GPP_leaf to the observed IAV of GPP were relatively independent. We conclude that our framework of decomposing GPP into LAI and GPP_leaf has a significant potential for facilitating future model intercomparison, benchmarking and optimization should be adopted for future data-model comparisons.

Spatial Pattern and Population Structure of Artemisia ordosica Shrub in a Desert Grassland under Enclosure, Northwest China.

Enclosure is an effective practice for restoring and rehabilitating the degraded grassland ecosystem caused by overgrazing. Shrub species, which are dominant in most desert grasslands in arid and semiarid regions, have some beneficial ecological functions for grassland restoration. However, how the population structure and spatial pattern of the Artemisia ordosica shrub changes in a grassland ecosystem under enclosed practice is not well understood. This study, conducted in the Mu Us desert in northwest China, was designed to measure the A. ordosica population according to the chronosequence of enclosure (enclosure periods ranged from 5 years, 10 years, 15 years, and 25 years), contrasting this with an adjacent continuously grazed grassland. The results showed that the enclosed grasslands had a higher number of individuals of different age classes (seedling, adult, aging, and dead group) and greater population coverage, but shrubs had significant lower (p < 0.05) crown diameter and height in comparison with those in continuously grazed grassland. Further, enclosed grasslands had a significantly higher (p < 0.05) Shannon-Wiener index (H) and Evenness index (E), but a significantly lower (p < 0.05) Richness index (R) than continuously grazed grassland. The crown of A. ordosica showed a significant linear positive correlation with height in all plots across succession, indicating that it was feasible to analyze the age structure by crown. The crown-class distribution structure of the A. ordosica population approximated a Gaussian distribution model in all survey plots. Within the population, seedling and adult groups exhibited aggregated spatial distribution at small scales, while aging and dead A. ordosica groups showed random distribution at almost all scales in different plots. The seedling A. ordosica group showed a positive correlation with adults at small scales in all plots except in 10 years of enclosure. However, it showed independent correlation with aging and dead groups at almost all scales. In long-term enclosed plots, the mortality rate of the A. ordosica population increased, therefore assistance management practices, such as fertilization, mowing, interval grazing, and seasonal grazing, must be employed to maintain population stability after long-term enclosure. This study can improve understanding and clarify the effects of enclosures in the desert grasslands of northwest China.

Topography and grazing effects on storage of soil organic carbon and nitrogen in the northern China grasslands

Soil on the earth has been estimated to sequester around 5.4% of total carbon (C), most of it as soil organic carbon (SOC), but the exact amount of and relevant mechanisms for the stock of SOC are far from clear. In this study, we assessed how topography and grazing influenced distribution of SOC, and soil total nitrogen (STN) in grasslands in the hilly and mountainous regions of northern China. Soil parameters (soil organic C and N content, pH value, gravel content, and bulk density in 50 cm soil depth) and topographic elements (slope aspect, position and inclination) were investigated at 171 sites. Results from model selection of generalized additive model (GAM) procedure showed the model with integration of topographic factors had strong predictability on the distribution of SOC and STN. This indicated that topography was an important driving factor for distribution of SOC and STN. Both SOC and STN storage were observed higher on shadow slopes and at the middle position of slopes. Although slope inclination had no direct effects on SOC and STN storage, it showed significant effects on soil pH value, gravel content and bulk density, which were significantly negatively correlated with stock of SOC and STN. Besides, the long history of grazing throughout the study area was also found to have significant negative effects on storage of SOC and STN, suggesting weakened relationship between topography and SOC and STN stocks. Our results indicate that topography, in combination with human activities such as grazing, has significant effects on storage of soil C and N either directly or indirectly via changing soil physico-chemical properties. Our study can help to understand the pattern of the topography effects on the storage of SOC and STN in grasslands with patchy distributions in the hilly and mountainous regions of the north China.

Seasonal changes of soil microbial C, N, P and associated nutrient dynamics in a semiarid grassland of north China

Semiarid grasslands are widely distributed in northern China and characterized by marked seasonality. While the role of soil microbes in nutrient cycling is known to be crucial, the nutrient dynamics in relation to changes and turnover of microbial pools over the growth season in semiarid grasslands, are not well understood. In this study, three grasslands with long-term traditional managements (enclosure from sheep grazing for 31 or 18 years, or continuous free overgrazing) were selected to investigate the seasonal fluctuations of microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP). In addition we calculated the turnover rates and fluxes of soil microbial biomass based on their seasonal fluctuations. Plant biomass and N, P uptakes were also assessed to reveal a potential relationship between plant and microbial nutrient pools. We found in this semiarid ecosystem approximately two times lower C:P and N:P ratios in microbial biomass (25:1 and 3:1, respectively) compared with global analysis (46:1 and 6:1, respectively). Enclosure from grazing increased MBC and MBN, while the change patterns of microbial pools were affected by season but not pasture management. Consequently, the turnover rates of microbial biomass as calculated from the seasonal fluctuations were similar in all treatments (around 1.5 year−1 for MBC and MBN, 3 year−1 for MBP). Lower mean stock in soil K2SO4-extractable N but similar in MBN compared with total plant N uptake were observed in all treatments, suggesting N deficiency in this region and the vital role soil microbes play as a stable nutrient pool for plant uptake. In contrast, both NaHCO3-extractable P and MBP stocks were much higher than total plant P uptake, suggesting no P deficiency under current N status.

Plant community responses to increased precipitation and belowground litter addition: Evidence from a 5-year semiarid grassland experiment.

Global climate change is predicted to stimulate primary production and consequently increases litter inputs. Changing precipitation regimes together with enhanced litter inputs may affect plant community composition and structure, with consequent influence on diversity and ecosystem functioning. Responses of plant community to increased precipitation and belowground litter addition were examined lasting 5 years in a semiarid temperate grassland of northeastern China. Increased precipitation enhanced community species richness and abundance of annuals by 16.8% and 44%, but litter addition suppressed them by 25% and 54.5% after 5 years, respectively. During the study period, perennial rhizome grasses and forbs had consistent negative relationship under ambient plots, whereas positive relationship between the two functional groups was found under litter addition plots after 5 years. In addition, increased precipitation and litter addition showed significant interaction on community composition, because litter addition significantly increased biomass and abundance of rhizome grasses under increased precipitation plots but had no effect under ambient precipitation levels. Our findings emphasize the importance of water availability in modulating the responses of plants community to potentially enhanced litter inputs in the semiarid temperate grassland.

Soil bacterial community composition and diversity in relation to edaphic properties and plant traits in grasslands of southern China

To identify the key roles and underlying mechanism for assembling soil microbial community structures at regional scales, we examined soil bacterial community compositions from 20 locations in a transect of grasslands of southern China. The bacterial community was sequenced for microbial 16S ribosomal RNA gene amplicons using Illumina MiSeq technology. The soil microbial community diversity was analyzed for plant, soil, geographic properties, and pure spatial distance based on a distance-based approach and with variation partitioning based on canonical redundancy analysis. The soil bacteria richness and alpha diversity index showed marginal positive relationship with plant richness and Shannon index. The bacterial community compositions of both the taxonomic and phylogenetic structures were best explained by the soil pH and plant diversity and soil nutrient availability, with the peak richness at pH 6.8. While the plant, soil and geographic factors were correlated with bacteria community dissimilarity, soil pH and plant diversity, nitrogen availability were relatively independent dominant community assemblage by quantifying taxonomic and phylogenetic turnover. Mantel tests indicated the assembly of soil bacterial community was predominated by the determinant processes. Overall, our findings suggest plant functional traits and abiotic soil properties (e.g., soil pH and inorganic nitrogen) collectively drive soil bacterial diversity patterns but are not limited by pure spatial distance in grasslands of southern China.

Reference gene selection for qRT-PCR assays in Stellera chamaejasme subjected to abiotic stresses and hormone treatments based on transcriptome datasets.

BackgroundStellera chamaejasme Linn, an important poisonous plant of the China grassland, is toxic to humans and livestock. The rapid expansion of S. chamaejasme has greatly damaged the grassland ecology and, consequently, seriously endangered the development of animal husbandry. To draft efficient prevention and control measures, it has become more urgent to carry out research on its adaptive and expansion mechanisms in different unfavorable habitats at the genetic level. Quantitative real-time polymerase chain reaction (qRT-PCR) is a widely used technique for studying gene expression at the transcript level; however, qRT-PCR requires reference genes (RGs) as endogenous controls for data normalization and only through appropriate RG selection and qRT-PCR can we guarantee the reliability and robustness of expression studies and RNA-seq data analysis. Unfortunately, little research on the selection of RGs for gene expression data normalization in S. chamaejasme has been reported.MethodIn this study, 10 candidate RGs namely, 18S, 60S, CYP, GAPCP1, GAPDH2, EF1B, MDH, SAND, TUA1, and TUA6, were singled out from the transcriptome database of S. chamaejasme, and their expression stability under three abiotic stresses (drought, cold, and salt) and three hormone treatments (abscisic acid, ABA; gibberellin, GA; ethephon, ETH) were estimated with the programs geNorm, NormFinder, and BestKeeper.ResultOur results showed that GAPCP1 and EF1B were the best combination for the three abiotic stresses, whereas TUA6 and SAND, TUA1 and CYP, GAPDH2 and 60S were the best choices for ABA, GA, and ETH treatment, respectively. Moreover, GAPCP1 and 60S were assessed to be the best combination for all samples, and 18S was the least stable RG for use as an internal control in all of the experimental subsets. The expression patterns of two target genes (P5CS2 and GI) further verified that the RGs that we selected were suitable for gene expression normalization.DiscussionThis work is the first attempt to comprehensively estimate the stability of RGs in S. chamaejasme. Our results provide suitable RGs for high-precision normalization in qRT-PCR analysis, thereby making it more convenient to analyze gene expression under these experimental conditions.

Optimal formula feed is a key for efficient transformation of forage to animal products in grass-based livestock husbandry

The animal husbandry in China can be categorized broadly into pastoral and farming animal husbandry. Grazing has long been a main form of animal husbandry in the pastoral areas. The lack of sufficient supply of high quality forage is a key factor that limits the development of animal husbandry in both the pastoral and farming animal husbandry. Natural grasslands in China have degraded seriously since 1970s due to overgrazing and global climate changes, exhibiting low productivity and poor ecological functions. Import of forages (mainly alfalfa and oat hay) from overseas (mainly USA and Australia) has increased markedly in recent years. The insufficiency for supply of high quality of forage and poor ecological function of natural grasslands are major issues limiting the social and economical development in large pastoral areas in China. How to develop a high-efficiency and environmentally-friendly animal husbandry has been a big challenge in these areas. The development of concept of “Grass-based Livestock Husbandry (GLH)” is novel in solving these problems by integrating the processes associated with grassland management, forage planting, forage processing and livestock feeding. More specifically, the GAH theory emphasizes that grasslands are of ecological importance with less function for forage production, while the production of high quality of forage will rely on the development of artificial pasture to sustain the livestock husbandry. Extensive efforts have been made to manage and restore the degraded grasslands, and develop artificial pasture with great yield, high quality and use efficiency of resources. In contrast, less attention has been paid to harvest, process, and store as well as utilize the forages for livestock husbandry in both pastoral and farming areas. In this paper, we discussed the effective ways to supply forage to livestock in both pastoral and farming areas. We further explored the technical solutions to improve the insufficient supply of forage in the two areas. We specifically highlighted the important roles of artificial pasture in provision of sufficient forage with high quality for livestock, thus protecting the natural grasslands and maximizing their ecological functions. Finally, we proposed that development of formulated forage systems with high efficiency is a crucial step for success in the grass-based livestock husbandry, and that green animal product is a main driver for development of ecological grass-based livestock husbandry in China. These theories and methodologies have great implications in development and practice of the grass-based livestock husbandry in both pastoral and farming areas.

Herbaceous phytoliths from forest and grassland in Northeast China: Potential significance for determining past forest–grassland boundaries

Phytoliths are a useful tool for reconstructing paleovegetation and paleoenvironments and grass short cell phytoliths (GSCPs), in particular, can provide important paleoenvironmental information. Although herbaceous phytoliths from non-grass species in forests also provide important paleovegetation information, they have not been investigated in as much detail as GSCPs, especially in Northeast China. In this study, we examined herbaceous phytolith morphotypes and assemblages from both forested and grassland areas in NE China, comprising three vegetation types. The phytoliths in 60 herbaceous quadrats were divided into seven morphotype groups. Cross-shaped phytoliths, bilobate type-C with long shank and papillate echinate morphotypes were only observed in grassland (GRA); complex saddle and bilobate type-A were only observed in non-understory vegetation in forested areas (NON); and phytoliths with scrobiculate decoration, elongate curved, silicified stoma (F), silicified stoma (D), globular granulate and oblong ruminate were only observed in forest understory (UND). Papillate (39.7%) was the dominant phytolith type in UND assemblages, and bilobate was dominant in NON (27.2%) and GRA (55.0%). According to the results of Discriminant Analysis (DA) and Detrended Correspondence Analysis (DCA), there was no similarity between UND and GRA, while NON had similarities with both UND and GRA. We conclude that herbaceous phytolith morphotypes and assemblages from forest and grassland in NE China are substantially different, which potentially enables their use for paleovegetation reconstruction in the region. Overall, our findings provide a new approach for determining past forest–grassland boundaries in NE China.

Reducing Uncertainties in Applying Remotely Sensed Land Use and Land Cover Maps in Land-Atmosphere Interaction: Identifying Change in Space and Time

Land use and land cover (LULC) data are a central component of most land-atmosphere interaction studies, but there are two common and highly problematic scale mismatches between LULC and climate data. First, in the spatial domain, researchers rarely consider the impact of scaling up fine-scale LULC data to match coarse-scale climate datasets. Second, in the temporal domain, climate data typically have sub-daily, daily, monthly, or annual resolution, but LULC datasets often have much coarser (e.g., decadal) resolution. We first explored the effect of three spatial scaling methods on correlations among LULC data and a land surface climatic variable, latent heat flux in China. Scaling by a fractional method preserved significant correlations among LULC data and latent heat flux at all three studied scales (0.5°, 1.0°, and 2.5°), whereas nearest-neighbor and majority-aggregation methods caused these correlations to diminish and even become statistically non-significant at coarser spatial scales (i.e., 2.5°). In the temporal domain, we identified fractional changes in croplands, forests, and grasslands in China using a recently developed and annually resolved time series of LULC maps from 1982 to 2012. Relative to common LULC change (LULCC) analyses conducted over two-time steps or several time periods, this annually resolved, 31-year time series of LULC maps enables robust interpretation of LULCC. Specifically, the annual resolution of these data enabled us to more precisely observe three key and statistically significant LULCC trends and transitions that could have consequential effects on land-atmosphere interaction: (1) decreasing grasslands to increasing croplands in the Northeast China plain and the Yellow river basin, (2) decreasing croplands to increasing forests in the Yangtze river basin, and (3) decreasing grasslands to increasing forests in Southwest China. Our study not only demonstrates the importance of using a fractional spatial rescaling method, but also illustrates the value of annually resolved LULC time series for detecting significant trends and transitions in LULCC, thus potentially facilitating a more robust use of remotely sensed data in land-atmosphere interaction studies.

Changes in multiple ecosystem services between 2000 and 2013 and their driving factors in the Grazing Withdrawal Program, China

Quantitative assessment of ecosystem services in the Grazing Withdrawal Program (GWP) of China is required to understand the effectiveness of environmental protection programs and the sustainability of grassland ecosystems. This study focused on quantitative assessment of changes of key ecosystem services and their driving factors in the GWP from 2000 to 2013. Based on widely used biophysical models, including the GLOPEM-CEVSA model, the precipitation storage method, Integrated Valuation of Ecosystem Services and Trade-Offs (InVEST), Revised Wind Erosion Equation (RWEQ) and Underground Productivity Model (UPM), this study integrated multi-source data to analyze dynamic changes of regulating services, including carbon sequestration, water regulation, sand fixation and soil retention, and the provisioning service of grassland yield. For the GWP area during 2000–2013, the ecosystem pattern remained relatively stable and multiple ecosystem services showed overall improvement but there were local deteriorations. For the 14 years net primary productivity (NPP) and grassland yield (GY) increased substantially. Water regulation in forest, grassland and wetland/water body ecosystems improved slightly. The soil conservation function of the entire ecosystem was slightly enhanced with soil retention showing an increasing spatial homogenization and wind erosion having a decreasing tendency. Ecological restoration and reconstruction efforts and climate change helped to improve ecosystem services. Increases in both temperature and precipitation and ecological rehabilitation had a positive effect on vegetation restoration related to a marked increase of vegetation coverage. Increase in annual precipitation increased rainfall related erosion but also assisted water regulation. Reduction in wind speed effectively lowered the occurrence of wind erosion. Vegetation restoration directly increased NPP and GY, and was conducive to water regulation and soil conservation. However, grassland degradation still continued in local areas. Ecological programs applied to the grasslands of China should be continued. Adopting adaptive management approaches that facilitate the synergy of multiple ecosystem services are required to maximize their benefit to the people of China.

Uncertainty in simulating regional gross primary productivity from satellite-based models over northern China grassland

Large-scale estimation of regional terrestrial gross primacy production (GPP) can improve our understanding of carbon cycle. However, model based estimates are subject to uncertainty. In this study, eight satellite-based models (i.e. VPM, TG, GR, VI, CFIX, ECLUE, VPRM and MODIS-GPP) were compared for GPP simulation in northern China grassland based on 17 site-year eddy covariance measurements, meteorological data and satellite data. Also, the regional spatial–temporal GPP patterns during 2001–2013 in northern China grassland were simulated and their uncertainties were quantified. The results showed that the model simulations exhibited significant correlations with observed GPP across these eight models and R2 or pseudo R2 ranged between 0.64 and 0.89 (p < .001), ECLUE model performed best. The annual grassland GPP had been growing in fluctuations from 2001 to 2013, with the averaged value of 241.8 g C m−2 a−1. Substantial spatial heterogeneity existed in grassland GPP, increasing from the west to the east. The disparities of satellite-based model structures resulted in the overall 49% relative uncertainty in regional simulation of GPP, which was high in area with arid dry climate. Our study highlighted the uncertainty traced back to model approaches under different environmental stresses (photosynthetically active radiation, soil water content and air temperature). For the accurate simulation of grassland GPP, uncertainty in alpine grassland and arid cold area on regional grassland GPP should be focused.

Patterns and determinants of the response of plant biomass to addition of nitrogen in semi-arid and alpine grasslands of China

Although the effects of adding nitrogen (N) to grasslands have been studied worldwide, little is known about how those effects are, in turn, influenced by climate, soil, and vegetation. Data from such experiments conducted in two main types of grassland in China, alpine and semi-arid, which differed widely in terms of climate, soil, and vegetation, were compiled and analysed to examine the response of above-ground biomass to N. Adding N increased the above-ground biomass by 51% on average. Although the response of biomass showed no obvious trend with the dose of N in the alpine grasslands, the response in the semi-arid grassland peaked at 15–20 g m−2 of N applied annually. Nitrogen addition efficiency in the alpine grasslands was higher than that in the semi-arid grasslands. The difference was mainly due to the differences in total soil N and its interactions with the above-ground biomass, which were particularly influenced by the soil's capacity to provide available N. These results suggest that soil N and features of local vegetation should be taken into account in arriving at the appropriate dose of N for a given site.

Mechanisms regulating the productivity and stability of artificial grasslands in China: Issues, progress, and prospects

China has 400 million hectares of grasslands, occupying 41.7% of the country’s total land area. Due to the overexploitation of grassland’s production functions and the neglect of its ecological functions, intensive livestock grazing in recent decades has resulted in widespread grassland degradation, reduction in ecosystem services, and imbalance between forage production and livestock demands in China. Compared to natural grasslands, artificial grasslands can increase forage yield up to 10–20 times. The development of high-quality artificial grasslands could fundamentally ease the severe shortage of forage supply, break the bottleneck in meat and milk production, curb grassland degradation caused by overgrazing, and thereby restore grassland ecological functions. Therefore, understanding the mechanisms that regulate the productivity and stability of artificial grasslands is a major national strategic need in order to transform the practices of sustainable livestock production based on the scientific and technological advancements, and to promote national ecological security, food security, and the development of ecological civilization. In this study, we examined theoretical basis underlying the regulations of artificial grassland productivity and stability, including theories of ecological stoichiometry, niche differentiation, compensation, mutualism, grazing optimization, and intermediate disturbance. Then, we reviewed current research status and the latest progress that has made in this field. Finally, we proposed fundamental research questions that need to be fully addressed in future studies, regarding the effects of stoichiometry of key nutrient elements, coupled water and nutrient availability, mutualism between forage species and soil microbes, and complementarity of functional traits and multiple forage species on plant carbon assimilation, growth, reproduction, forage quality, biomass allocation, primary productivity, and ecosystem stability. We also highlighted several key biological and ecological mechanisms regulating the productivity and stability of artificial grasslands.

Responses of green-up dates of grasslands in China and woody plants in Europe to air temperature and precipitation: Empirical evidences based on survival analysis

Responses of green-up dates of grasslands in China and woody plants in Europe to air temperature and precipitation: Empirical evidences based on survival analysis

中国东部草原植被绿度时空变化分析及其对煤电基地建设的响应

中国东部草原植被绿度时空变化分析及其对煤电基地建设的响应

Quantification of year-round methane and nitrous oxide fluxes in a typical alpine shrub meadow on the Qinghai-Tibetan Plateau

Alpine meadows are the largest grasslands in China. Greenhouse gas exchanges between alpine meadows and the atmosphere are highly uncertain due to the lack of year-round flux measurements. In this study, the methane (CH4) and nitrous oxide (N2O) fluxes in an alpine Potentilla fruticosa shrub meadow in the Qinghai-Tibetan Plateau were investigated using the static, opaque chamber-gas chromatography method between April 2012 and April 2015. The annual CH4 uptake (1.33–1.35 kg C ha−1 yr−1) and Q10 value (1.79) were at the low end of the range for natural grasslands in China, which indicated that global warming at the same extent would result in less of an increase in the CH4 sink in the Qinghai-Tibetan Plateau, compared to other grassland areas. The N2O emissions during the spring thaw period showed a tremendous inter-annual variation (0.03 to 0.14 kg N ha−1), which was closely linked to the variation in annual precipitation, especially the precipitation of the previous growing season. The high substrate concentrations and soil moisture during the spring thaw periods together provided the conditions for pulse N2O emissions. When the pulse N2O emissions occurred, emissions from the non-growing seasons dominated (67–74%) the annual total emissions. Thus, a proper sampling frequency (daily to weekly measurements) in non-growing seasons was needed for the quantification of annual fluxes. Four gas chromatographic set-ups (the Ar-CH4, N2-ascarite, N2-CO2, and pure N2 methods) were adopted for N2O flux measurements over natural grasslands in China. Using the N2-CO2 method, the annual N2O emissions from the alpine shrub meadow were quantified to be only 0.18–0.27 kg N ha−1 yr−1 in the present study. Based on measurements using the first three of the four gas chromatographic set-ups, the conclusion that can be drawn is that unfertilized natural grasslands in China function as marginally weak N2O sources, whereas the pure N2 method may remarkably overestimate the emissions.

Optimization schemes for grassland ecosystem services under climate change

Ecosystem and associated services in arid and semiarid areas are sensitive to climate change and human activities. Guiding human activities based on the optimization of ecosystem services can help humans adapt to climate change effectively, which is vital for regional sustainability. We evaluated the distribution of five ecosystem services: net primary productivity (NPP), soil conservation (SC), water yield (WY), water retention (WR), and livestock supply in the grassland and agro-pastoral transitional zone of China (GAPTZ) under the future climate scenarios of representative concentration pathway (RCP) 4.5 and RCP8.5 in 2050. We designed the four grazing-intensity scenarios of ungrazed (UG), lightly grazed (LG), moderately grazed (MG), and heavily grazed (HG) and analyzed the impacts of climate change and grazing on the ecosystem services. Finally, we presented the optimization schemes of grazing intensity in the GAPTZ under the objectives of “strong sustainability” and “weak sustainability”. “Strong sustainability” objective means that the total change rate of ecosystem services compared to the ungrazed scenario is maximal and should not be less than 0. “Weak sustainability” objective means that the livestock supply is preferential and the total change rate of ecosystem services compared to the ungrazed scenario is maximal but could be less than 0. The results showed that both climate change and grazing exert great influence on the supply and interrelation of ecosystem services. In the northeast of the GAPTZ, LG and MG can stimulate grassland to tiller and enlarge ecosystem services integrally. HG has the severest negative effect on ecosystem services overall. Under the “weak sustainability” objective, LG can be widely adopted in the GAPTZ. Under the “strong sustainability” objective, grazing should be limited in the northwestern and north-central GAPTZ. Reasonable planning of grazing intensity and its spatial patterns can promote effective utilization of grassland resource and realization of regional sustainability.